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[adriaticum]

Hello,
I've been trying to figure this one question about Oncorhynchus Mykiss.
If rainbow trout and steelhead are the same species and live in mostly the same habitat, at what point in their evolution did one group decide to take a swim in the ocean and split off from the others?
Or did they really live in the ocean first and then some of them decided to stay after spawning and said bye, bye to the rest?
Does anyone have any idea?

Thanks

P.S.
And when a steelhead passes a rainbow trout in the river, does it say hi?

[mastercaster]

I think they say.  "Hi chum" unless i'm thinking about some other species

[coryandtrevor]

The waitress at the Cactus Club on #3 Road in Richmond informed me that their new "Steelhead Salmon" on the menu come from....wait for it...."like... they're salmon from Steelhead Lake or something, and don't worry it's not trout" ( rolls her eyes).

Almost burst out laughing !!!!!!!

Anyway,

Steelhead vs. Rainbow Trout

Rainbow trout and steelhead are the same species of fish; the two names reflect two distinct life history patterns. The name rainbow trout is used for the non-anadromous life history. Rainbow trout do not leave the stream to go to the ocean. They spend their entire life in the stream. The name steelhead refers to the anadromous life history described above.

Anadromous steelhead and resident rainbow trout did not arise from two distinct evolutionary lines. There is a close genetic and taxonomic relationship between these two forms. Anadromous forms of the trout can convert to resident populations when drought events or damming of rivers blocks their access to the ocean. Conversely, resident trout populations can become anadromous if ocean access becomes available. It is typical to have both life history patterns occurring in the same stream. In fact, resident and anadromous parents can produce offspring of both varieties. It has been speculated that there is a food availability related trigger which determines whether a particular fish emigrates to the ocean or remains in the stream. It may be that if there is abundant food in the stream and a fish is growing at a rapid rate, it will remain in the stream. If food is limited and growth is slow, the fish will have a tendency to emigrate.

This dual life history pattern of steelhead and rainbow trout makes the species more adaptable to changing environmental conditions. At the southern most limits of steelhead distribution this is particularly important due to unstable, variable climatic and hydrographic conditions.

Source: Steelhead Restoration and Management Plan for California, by Dennis McEwan and Terry Jackson, CA Department of Fish and Game

[adriaticum]

Thanks for your reply, it's great.